Police sources said two grenades were hurled by two motorcycle riders at Gashbari daily market near Goreswar at a around 6.10 pm injuring four persons on the spot.
Police went to the site and the injured were taken to hospital.
The identity of those who hurled the explosives has not been established, they said.
The anti-talk NDFB (Songbijit) faction is active in the area.
Two grenades were lobbed towards the crowded area.